@Happily_Grim
Even if it's the most recent chapter I tend to just click the page as a way to get back to the series page, and then check comments.
For some the flow might be this:
[ul][*]From follows, open the chapter in a new tab
[*]Done reading, at credits pages, want to read comments -> click chapter comments button in reader so as not to have to load the series page
[*]Done reading, at credits pages, don't want to read comments -> immediately close tab so as not to have to load the series page[/ul]
Could always add a preference for how it's tracked in the settings, though. That way it could be tailored to reading style.
More options are always nice, but in a case like this (esp. with a UI change like a three-state reading marker, the ramifications of just that UI element are already a whole thing) the code for doing it each way are radically different it's not worth dealing with resulting bugs and having code for the same action possibly be in multiple places